Hi,
Do you want to add a new probe to an existing serverfarm without interrupting the serverfarm?
This can be done without any problem.
Configure your new probe and add it under your serverfarm:
serverfarm farm
probe new-probe
You can monitor this by doing sh probe new-probe detail and show serverfarm farm detail.
Do keep in mind that if for some reason your new probe fails (fe a misconfig), your rservers in your serverfarm will go down!
HTH,
Dario